Root canal filling materials are an essential material in the endodontics and after thoroughly removing off staining substances in a root canal, they are filled in the root canal. A typical example of such root canal filling materials is a generally called guttapercha point having such a shape that it is fit to the shape of the root canal and that it is provided at the end terminal thereof with a taper shape so as to make the filling easy. The guttapercha point includes the following two types: a master point (main point) type and an accessory point type.
The master point type is formed in accordance with the international standard and is applied for the filling in a main portion of the root canal which has been reamed by means of a root canal reamer having the same dimension defined in the international standard, such as a reamer, a K-file, and an H-file.
Since the root canal shape is circular in the vicinity of a root apex which has been reamed but non-circular in many of other portions thereof, the accessory point is used in a lateral condensation method by which it is filled in a void portion formed after filling the master point, to make it free from any dead space. Properties necessary for the root canal filling point are that it is appropriately flexible, is tough, and is compressible. Further, it is required to have properties that it has a good adhesion to the root canal wall and can be burnt out or removed by a heat cutter.
In addition, a temporary filling material is filled under pressure in a deficient portion of the tooth upon heating and softening and is supplied in the form of a rod or a pellet. Further, the temporary filling material is used for temporary filling before a permanent filling material has been filled, and when a dental pulp damage is large, it is used for filling until the damage has been completely recovered such that the permanent filling material can be filled. During this period of time, the temporary filling material completely protects a dental cavity and does not cause any change in the position relation of neighbour teeth or opposing teeth. Necessary properties as the temporaty filling material are that it is free from irritation, toxicity, and harms to other properties, does not have solubility and is appropriately tough and resistant to abrasion. Further, it is required that it flows upon softening and pressure contacting and well adheres to the dental cavity and that it can be readily removed after it has been used.
Hitherto, in order to meet the foregoing requirements, guttapercha which is collected from a tree of the sapodilla family living in the tropics and zinc oxide have been used as main components in the dentistry. These components are formed in the form of a narrow point provided with a taper shape and then filled in the root canal so as to fit to the dimension of a reamed root canal. Alternatively, after adjusting the softening operation property by the addition of a wax and other additives to the guttapercha and zinc oxide, the mixture is formed in the form of a rod or a pellet to apply the temporary filling of a dental deficient portion.
However, since guttapercha collected from a tree has a low tensile strength and is too soft, when the resulting filling material is used as a root canal filling point, it is weak, i.e., it has a small deforming stress and in particular, a narrow point is immediately bent, whereby it is especially difficult to fill it into a curved narrow root canal. Further, when it is exposed to direct rays of the sun or in air for from several months to several years, the rubbery properties of the guttapercha are deteriorated, and the point becomes brittle, whereby it is likely to be broken or it causes a blooming phenomenon by which a power generates on a surface thereof.
Further, in the case that large amounts of a wax and other additives are blended for the temporary filling, when stored over several years, the was blended is separated to cause a phenomenon that it sticks to fingers, whereby the operation becomes difficult. Still further, it causes a poor softening property and becomes so brittle that it is likely broken, whereby the material is no longer practically usefull.
In view of the above, so far as natural guttapercha is used, scattering in the quality of the raw material is great, and it is quite difficult to keep a stable quality.
Moreover, there are cases that the material is placed in various circumstances concerning the temperature are humidity after the production and then provided to the dentist for the dental treatment (there may be even a case that it is used for the dental treatment after a lapse of time of several years) and, therefore, among the products, there are ones that cannot be suited for the use. Thus, various claims for clients have been generated.
The natural guttapercha contains trans-1,4-polyisoprene as a main component but is incorporated with foreign components such as other natural resins and impurities. These foreign components are varied depending upon the place of production, and there formulations have not yet been completely clarified. Accordingly, it is impossible to get the starting material of a stable quality, and so far as the natural guttapercha is used as a main component for the dental filling, such problems as those described above are inevitable.
The guttapercha is never domestically yielded in Japan and, therefore, its availability relies on the importation. However, the availability of the guttapercha tends to be affected by the state of affairs in Southeast Asia as the place of production and, therefore, not only its price is considerably expensive, but also a variation in quality is quite vigorous. Thus, a stable supply of guttapercha is for the moment rather difficult.